1. Field of the Invention
This invention relates to a sheet feed device for use in a sheet counter and, more particularly, to an improvement in sheet transport/separation performance whereby damage to sheets is prevented.
2. Description of the Related Art
In general, sheet counters for counting the number of sheets of paper, such as bank notes, bills, slips, and labels (hereinafter referred to simply as sheets), have a construction in which a bunch of sheets are placed on a hopper, sheets are separated and transported therefrom one by one by a separation roller and a roller having a friction surface formed as a part of its circumferential surface, and the number of sheets is detected while the sheets are transported. The counted sheets are stacked in a certain sheet accommodation section (stacker).
In a sheet feed device of this kind of sheet counter, if the sheet feed device is arranged to prevent double-feed of sheets by the effect of friction, the differences between various frictional forces, such as
(1) a frictional force produced between the feed roller and the sheet, PA1 (2) a frictional force produced between the sheets, and PA1 (3) a frictional force produced between the sheet and the separation roller,
are utilized. To produce the differences of such forces, a sheet separating mechanism (a mechanism for preventing double-feed) is constructed so as to have a gap such that the force applied to two or more sheets passing therethrough is substantially large, while the force applied to one sheet is not so large.
This frictional force is produced by a method of applying a force to a small area or a method of applying a force to a thin linear portion with respect to a time point during the passage of each sheet.
For example, a technique for producing such a frictional force from a force applied to a very small area by the former method is disclosed in Japanese Patent Laid-Open Publication No. 59-153732. The technique disclosed in this publication relates to an arrangement using, as shown in FIGS. 1 and 2, a feed roller 5 having a friction surface A and a non-friction surface B formed in its circumferential surface and mounted through a feed shaft 10 so as to be driven with a motor, a take-in roller (guide roller) disposed in a front position above the feeding side of the feed roller 5 so as to be able to contact a sheet 9, and a separation roller 6 disposed at a rear position so as to face a recessed portion 8 of the feed roller 5 with a gap defined therebetween, through which only one sheet 9 can pass. The separation roller 6 and the take-in roller (guide roller) are linked by a gear. A one-way clutch is also provided to prevent the separation roller 6 from rotating in the sheet feeding direction when sheet 9 is introduced into the gap at the separation roller 6.
A technique for producing a frictional force from a force applied to a linear portion by the latter method is disclosed in Japanese Patent Laid-Open Publication No. 63-64194. The technique disclosed in this publication relates to an arrangement in which, as shown in FIGS. 3 and 4, a separation roller 6 is disposed so that its rotation shaft 11 is generally perpendicular to a feed shaft 10 of a feed roller 5 unlike the separation roller 6 in accordance with the former method, and is formed so as to have a predetermined axial length, and in which the separation roller 6 is opposed to a recessed portion 8 of the feed roller 5 generally perpendicularly, so that the amount of lapping of the separation roller 6 and the feed roller 5 is increased.
In the sheet separating mechanisms of the thus-constructed sheet feed devices, the frictional force for separating each sheet is proportional to the applied force, and therefore the same force may be applied to obtain the same sheet separating ability (i.e., the ability of preventing double-feed). Consequently, in the former and latter arrangements, the force applied per unit sheet area is very large if applied force/area is considered, and various problems described below are therefore encountered.
In the case of the former (Japanese Patent Laid-Open No. 59-153732), the shafts 10 and 11 for the feed roller 5 and the separation roller 6 are disposed parallel to each other so that the separation roller 6 is positioned in the rectangular recessed portion 8 of the feed roller 5. Also, in the lapping relationship between a separation surface 7 on the circumference of the separation roller 6 and a roller surface 4 on the circumference of the feed roller 5, a point of contact between the feed roller 5, the separation roller 6 and the sheet 9 at a certain time point is virtually a geometrical point and the amount of lapping of the feed roller 5 and the separation roller 6 is small, so that the force of pressing the sheet 9 by the separation roller 6 at the time of sheet separation is very large. In other words, a pressing force is applied to the sheet 9 by the contact with edges 8a of the recessed portion 8 of the feed roller 5 and with edges 7a of the separation surface 7 of the separation roller 6, as indicated by the arrows in FIG. 2. The sheet receives a particularly concentrated load from the edges 7a of the separation roller 6.
There is therefore a problem in that the pressing force from the edge 7a of the separation roller 6 contacting the sheet 9 generally perpendicularly can easily cause an impression of creasing of the sheet in a direction corresponding to the direction in which the sheet is transported (a crease line or an elongated recess having the same width as the roller ) if the sheet is new. If sheets in which such a crease line is formed are counted again by being reversed, the crease line is reversely changed into a line of protrusion, that is, the creased portion of the sheet is flapped by the separation roller 6 at the entrance of the sheet separating mechanism, so that the end of the creased portion of the sheet is ripped. Thus, there is a second problem of such a further damage to the sheet.
If there is an ink or a pencil material of a print or letters on the sheet, the separation roller 6 contacts this material to cause flowing of the print or the letters, thereby seriously contaminating the sheet surface. Further, the image on the sheet may be transferred to the separation surface 7 of the separation roller 6 and may be transferred again to the surface of another sheet, resulting in the formation of a thick stripe corresponding to the thickness of the separation surface 7 of the separation roller 6 on the sheet surface. There is a third problem of the appearance of the sheet being impaired in this manner.
The separation surface 7 of the separation roller 6 acts to impose a large load upon the sheet 9, as mentioned above. There is therefore a fourth problem of the edge portions 7a being easily worn unevenly, although they are rotated to avoid unevern wear.
Further, if sheets once creased, relating to the above-described problem, i.e., sheets curved along the shape of the separation roller 6 at the sheet separating mechanism or repeatedly counted sheets, are introduced, it is possible that the shape of the separating portion of the sheet separating mechanism will coincide with the curved shape of such sheets, and the sheets can pass through the mechanism without being separated in such a situation, that is, can be transported in a superposed state.
On the other hand, in the sheet separating mechanism of the latter type of arrangement (Japanese Patent Laid-Open No. 63-64194), the separation roller 6 has a roller shape with the roller separation surface 7 facing the rectangular recess 8 of the feed roller 5. In the lapping relationship between the separation surface 7 on the circumference of the separation roller 6 and roller surface 4 on the circumference of the feed roller 5, a point of contact between the feed roller 5, the separation roller 6 and the sheet 9 at a certain time point is included in a line of contact. Therefore, the amount of lapping of the feed roller 5a and the separation roller 6 is a largely increased in comparison with the former arrangement, so that the sheet 9 separating ability is improved and unevern wear of the separation surface 7 can be prevented by rotating the separation roller 6. Thus, improvements with respect to the above-mentioned fourth and fifth problems of the point-contact sheet separation can be achieved.
In this arrangement, however, a considerably large pressing force is applied to the sheet 9 at positions where the sheet 9 faces the edges 8a of the rectangular recessed portion 8 the feed roller 5, as indicated by the arrows in FIG. 4, since the separation roller 6 is arranged to separate sheets by line-contact based on being positioned in the recessed portion 8 of the feed roller 5, although the separation roller 6 has a circular-arc surface capable of entering the recess B. Consequently, the above-mentioned first to third problems of the former arrangement (crease, ripping, contamination and so on) are still left although small improvements with respect to these problems have been achieved.